In the trend of smaller package and higher input/output (I/O) counts, a finer pitch is needed for a flip-chip bump on trace (BOT) package. The finer pitch requirement causes bump dimensions to shrink. As such, the area of metal/solder interface (metal bump) and solder/trace joint interface also decreases. So, electromigration (EM) resistance at both “bump-to-trace” and “trace-to-bump” sites get worse due to higher current density.
Corresponding numerals and symbols in the different figures generally refer to corresponding parts unless otherwise indicated. The figures are drawn to clearly illustrate the relevant aspects of the embodiments and are not necessarily drawn to scale.